The present invention relates to an engine control apparatus and, more particularly, to an electronic control apparatus using, for example, a microcomputer so as to effectively perform control operations such as arithmetic control of fuel injection quantity.
When an engine is controlled by a conventional electronic control apparatus using a microcomputer, the operating state of the engine is always monitored, and the proper fuel injection quantity corresponding to the operating state is calculated to control fuel injection.
Conventional means such as an engine speed sensor, an engine temperature sensor and a throttle valve opening sensor are used to monitor engine operating states. In addition, an intake air flow measuring unit is known, and is a device directly associated with an arithmetic operation of fuel injection quantity. Such a device is exemplified by a heat wire type air flow sensor. This sensor comprises a temperature sensing element arranged in an intake pipe and controlled by heating power. The element radiates heat due to the air flow in the intake pipe. Therefore, when the temperature sensing element is energized, its temperature characteristics correspond to an intake air flow rate.
An electronic engine control unit comprises, for example, a microcomputer. In order to calculate the proper fuel injection quantity corresponding to a given engine operating state in such a control unit, it is desirable that an engine operating state detection signal supplied thereto be digital data. Accordingly, it is also desirable that the air flow rate signal from the air flow rate measuring unit be a digital signal.
In view of this, it is proposed to obtain an air flow rate signal as a pulse signal and represent a measured air flow rate by a pulse width of the pulse signal. When such a signal is given, the intake air flow rate can be numerically detected by counting clock pulses representing the pulse width. The resultant digital data can be effectively utilized for arithmetic control in the microcomputer.